The long-term goal of this project is to improve integrated pest management (IPM) practices for cereal aphids in wheat, barley, and sorghum in the United States. To achieve this goal, we will increase the knowledge of aphid host plant resistance and natural enemies for IPM programs and provide fundamental knowledge of cereal aphid biology and ecology. Over the next 5 years we will focus on the following objectives: OBJECTIVE 1: Determine regional distribution and significance of invasive aphid species on cereals and alternate grass hosts, discover changes or shifts in the populations, generate relevant phenotypic information, and work with breeders or geneticists to map and pyramid resistant genes. Subobjective 1A: Determine the biotype diversity of the S. Maydis known as the hedgehog aphid (HGA) in cereals and native grasses in advance of discovering and utilizing resistant sources used in breeding for resistance. Subobjective 1B: Identify wheat germplasm resistant to HGA, as well as wheat accessions resistant to all U.S. RWA biotypes. Subobjective 1C: Characterize RWA and HGA resistance genes and develop molecular markers for their introgression into locally adapted breeding lines and cultivars. OBJECTIVE 2: Determine the biological differences and interactions among available sugarcane aphid resistance genes, including comparisons of cross-resistance genes, elucidate resistance mechanisms, and work with breeders and geneticists to map, pyramid, and deploy resistant genes. Subobjective 2A: Develop forage sorghum germplasm resistant to sugarcane aphids. OBJECTIVE 3: Develop effective multi-scale aphid infestation monitoring and sampling technology, develop geographically explicit cereal aphid pest infestation risk models, and elucidate and integrate field and landscape-level components of the natural enemy populations into improved management systems for invasive cereal aphids. Subobjective 3A: Use field research methods and statistical modeling and hypothesis testing to develop a detailed understanding of spatial and temporal factors that determine colonization, population dynamics, and community development of aphid natural enemies in grain sorghum fields and their importance for sugarcane aphid biological control. Subobjective 3B: Develop and disseminate new, time-efficient, and statistically accurate and precise methods for sampling aphid natural enemies in sorghum.
The combined annual economic value of wheat, sorghum, and barley within the United States is over $16 billion. Cereal aphids are major pests of world agriculture that vector numerous plant viruses and remove photoassimilates by inserting their mouthparts into the sieve elements of the phloem tissue. The direct loss from feeding and the transmission of viral diseases during the process of feeding make cereal aphids the most significant threat to U.S. cereal crop producers. Although aphids in general are small in size, the reproductive potential is at the higher end of the spectrum when compared to all arthropods, with exponential increases and short generation times. Significant yield reductions occur from the direct effect of endemic or epidemic aphid populations. New information on the factors affecting insect populations and new integrated pest management (IPM) tools, control technologies, and aphid-resistant germplasm are needed in order to advance sustainable IPM programs for cereals. The objectives of this project that will deliver the associated products to the consumer are to: 1) determine the biotypic diversity in aphid populations which threatens deployment of aphid-resistant cereals; 2) identify new sources of resistance to aphids in wheat and sorghum and barley; 3) determine the extent and severity of new aphid pest species attacking cereal crops; and 4) develop or refine methods for detecting and monitoring aphid infestations to optimize biocontrol in cereals. The specifically designed research provided in this plan will increase our knowledge on the genomics of virulent cereal aphid biotypes within the U.S. and increase the knowledge of available genetic sources of resistance in wheat, barley, and sorghum. Once identified these resistant sources will be introgressed into available breeding lines. In addition, the benefits and ecological associations of beneficial insects in the agricultural landscape will be better understood and utilized as a result of areawide studies on these organisms.
Under Objective 1A: The USDA-ARS Stillwater, Oklahoma laboratory screened spring and winter barley entries with known greenbug (GB) and Russian wheat aphid (RWA) resistance genes in them to identify sources (genes) that would also express resistance to hedgehog grain aphid (HGA). From this work, two sources of winter barley 00BX 11-115, and Post 90 both have the Rsg1 gene that expressed cross-resistance to HGA. Through the evaluation Winter Barley’s 00BX 11-115 and Post 90, we discovered that both contain the Rsg1 expresses greater antixenosis (fewer aphids/seedling), significantly lower plant damage ratings, and significantly lower reproductive potential when compared to all other entries. The study found that at least in the seedling stage, the Rsg1 GB/RWA resistance gene confers cross-resistance to HGA. This finding is also landmark in that it will provide a possible differentiation for discovering new HGA biotypes. Under Objective 1C: Our laboratory has screened a large set of germplasm, and identified 14 accessions resistant or highly resistant to all five major U.S. RWA biotypes. We further confirmed these resistance sources and selected 6 accessions with superior resistance, including PI 626581, PI 626575, PI 626582, PI 625154, PI 625142, and PI 625139, for gene mapping and mapping/breeding populations are being developed. Crosses were also made to transfer Dn10, a new RWA resistance gene we identified recently, to Oklahoma wheat breeding lines. We began to screen germplasm for HGA, and about 1700 accessions from the NSGC Winter Wheat Core Set will be screened by the end of 2021. Under Objective 2A: In collaboration with ARS researchers in Lubbock, Texas, previously registered and released 2 sugarcane aphid resistant parental lines that expressed antibiosis and tolerance when challenged by the sugarcane aphid. Both lines were developed using the pedigree method of plant breeding and are confirmed to be restorer lines. These same two lines labeled LBK1 and LBK2 were more recently used to develop 2 male sterile lines through backcrossing and using the A3 cytoplasm male sterile technique where sugarcane aphid resistant forage sorghums have now been developed, which is the main objective for 2A. Under Objective 3A: Field research for the year one of this project is currently underway. All experimental grain sorghum plantings have been made and collaborating grower’s fields have been identified. Research protocols were implemented in collaborating grower’s fields in mid-June and in experimental plantings beginning in early July. Laboratory research on sugarcane aphid natural enemy efficacy is underway with the parasitoid Aphelinus nigritus. We are currently investigating attack rates and preference for sugarcane aphid and greenbug on grain sorghum. Under Objective 3B: Experimental grain sorghum plantings were established and research on developing sampling for sugarcane aphid natural enemies in grain sorghum has been initiated. The subordinate project, ‘Areawide Pest Management of the Invasive Sugarcane Aphid in Grain Sorghum’, supports Objectives 2 and 3 of the parent project by providing a direct outlet for technology and information. The following progress was made on the Areawide Pest Management of the Invasive Sugarcane Aphid in Grain Sorghum. Under Objective 4, two sorghum growing areas in South Texas, one of susceptible sorghum consisting of 8,240 acres and the other of resistant sorghum consisting of 2,850 were intensively monitored weekly for sugarcane aphid and natural enemies for the fourth and final year. As in previous years, the resistant area showed lower sugarcane aphid populations and reduced damage. Under Objective 5A, grain sorghum and forage sorghum lines were screened in the greenhouse as in previous years and resistance and agronomic characteristics. Research on genetic mapping of resistance genes and phenotyping studies continued. Quantitative trait loci (QTL) were identified that are associated with the resistance to sugarcane aphid. In addition to advancing breeding lines from crosses, the sorghum association panel was evaluated for aphid resistance for the third year under the field conditions. Under Objective 5B, a spatially explicit, individual-based, stochastic model that integrates the life cycle and aero-ecology of sugarcane aphid to forecast regional infestations of sorghum fields was refined and tested to assess sensitivity and accuracy of estimates of northward aphid migration on wind. Under Objective 5C researchers continued to evaluate synergism of aphid-resistant hybrids and insecticide application. Under Objective 6, multiple presentations about sugarcane aphid management and programs were made to grower groups, Extension Educators, and other professionals. Under Objective 7, Oklahoma State University researchers continued development of a spatially explicit economic model coded in the General Algebraic Model System environment with an interface and linkages with Geographic Information Systems ArcMap software.
Lindenmayer, J.C., Payton, M., Giles, K.L., Elliott, N.C., Knutson, A.E., Bowling, R., Seiter, N.J., McCornak, B., Brown, S.A., Royer, T.A. 2021. Evaluation of two-leaf sampling units to estimate sugarcane aphid (Hemiptera: Aphididae) economic thresholds in commercial grain sorghum. Journal of Economic Entomology. 114(1):481-485. https://doi.org/10.1093/jee/toaa270.
Wang, H., Grant, W.E., Koralewski, T.E., Elliott, N.C., Brewer, M.J., Westbrook, J.K. 2020. Where do all the aphids go? A series of thought experiments within the context of areawide pest management. Agricultural Systems. 185:102957. https://doi.org/10.1016/j.agsy.2020.102957.
Giles, K.L., Elliott, N.C., Butler, H.E., Baum, K.A., Backoulou, G.F. 2021. Increase in importance of Aphelinus nigritus (Howard) on winter crops in Oklahoma coincides with invasion of sugarcane aphid on sorghum in Oklahoma. Southwestern Entomologist. 46(1):59-68. https://doi.org/10.3958/059.046.0105.
Vitale, J., Vitale, P.P., Epplin, F., Giles, K., Elliott, N.C., Peairs, F., Burgener, P., Keenan, S. 2020. Farm management practices used by wheat producers in the western Great Plains: Estimating their productivity and profitability. Journal of Applied Farm Economics. 3(1).
Koralewski, T.E., Wang, H., Grant, W.E., LaForest, J.H., Brewer, M.J., Elliott, N.C., Westbrook, J.K. 2020. Toward near-real-time forecasts of airborne crop pests: Aphid invasions of cereal grains in North America. Computers and Electronics in Agriculture. 179:105861. https://doi.org/10.1016/j.compag.2020.105861.
Elliott, N., Giles, K., Brewer, M., Szczepaniec, A., Knutson, A., Michaud, J.P., Jessie, C., Faris, A., Elkins, B., Wang, H., Koralewski, T., Grant, W. 2021. Recruitment of natural enemies of the invasive sugarcane aphid vary spatially and temporally in sorghum fields in the southern Great Plains of the USA. Southwestern Entomologist. 46(2):357-372. https://doi.org/10.3958/059.046.0207.